Audio frequency amplification



March 2, 1937. A. D. LASSITER I AUDIO FREQUENCY AMPLIFICATION I Original Filed Dec. 9, 1931 Patented Mar. 2, 1937 PATENT OFFICE UDIO FREQUENCYVAIVIIPLIFICATION 7 Application men. I ias siter, Philadelphia, Pa.

December'9, 1931, Serial No. 579,972 Renewed May 22;1936- 2 Claims. (01. 179-1003) This invention relates to new and useful improvements in electrical wave amplifiers, particularly to the audio-frequency type.

An object of the invention is the amplification of audio signals from radio or television detectors, voice pickups, microphones, and variable area or Variabledensity recording on film, in a much more efficient manner than is now possible with present day apparatus, and it is so constructed that it furnishes direct current to a part thereof, thereby allowing any reproduction of the low register in sound recording below one hundred and thirty cycles which is a decided improvement over any other alternating current operated power amplifier, which cannot reproduce an audio signal of lower frequency than the alternating current frequency.

Another important object of the invention is the provision of an adjustable input impedance for eliminating undesirable oscillations, and distortions due to any regenerative reaction.

Other objects and advantages will become apparent to the reader of the following specification.

The single figure of the drawing represents a diagrammatic view of an audio-frequency amplifier circuit and a diagrammatic view showing a four-stage audio-frequency amplifier employing the special insulated core transformer and disclosing the adjustable input impedance, resistant coupled amplifiers, and the insulated core transformer in wired connection. Also, a diagrammatic view of the direct current supply furnished to the first heater elements of the first two amplifying vacuum tubes and a four ampere direct current supply at eight volt pressure when an exciter lamp is desired for the translation of sound light rays from film recording thereby eliminating the use of batteries and it is made automatic for a dual operation.

Referring to the drawing wherein like numerals designate like parts, it can be seen that the invention shown in the figure is of the four stage power amplifier type. Numerals I and 2 represent the input circuit connected at one side to a common ground, while the other side 4 and 5 connects to a 50,000 ohm dual potentiometer which furnishes plate current to light sensitive cells with variable terminals on each side connected to a five-electrode vacuum tube 24, which is a direct coupling between the tunable input circuit and the first amplifying device 24. It is to be understood that the two light sensitive cells are to be connected one to the taps l and 5 and the other to the taps 2 and 4. Numerals 3 and 6 represent the eight-volt four ampere direct cur-. rent supply with dualswitch for using two exciter lamps. The dualpotentiometer will serve to fade out one or the other of the light sensitive cells while the switch will bring in or disconnect the corresponding exciter lamp. The connections for these are understood in the art as being similar to those heretofore used with batteries. It will be noted that in my application, substantially smooth direct current is supplied to the tubes 24 and 21 by the transformer 29, the rectifier 33 and the choke coils in the circuit to these tubes. The source of current for the exciter lamp passing through the dual potentiometer switch is derived from this same direct current supply and serves to give a proper working current to one or the other of the exciter lamps.

The second stage employs a four electrode vacuum tube 21, resistant coupled to the first tube 24. The output of the second tube 21 is resistance coupled for transferring energy to addi tional circuit devices, such as amplifiers in any number. The amplified audio-frequency signals are transferred to the third circuit by means of resistors and capacities which serves as the input to the third amplifying circuit which involves a four electrode vacuum tube numeral 28.

The amplified audio frequency signals are transferred to the fourth amplifying circuit by means of an audio frequency transformer, the secondary of which serves as an input to the fourth amplifying circuit which involves one three electrode vacuum tube.

The output of this fourth stage is coupled to the primary of an audio frequency transformer numeral 9, which serves to pass the amplified audio-frequency currents from the vacuum tube 50, to the loud speaker (not shown).

It can be seen that by employing a low impedance audio-frequency output transformer, the

The filaments of the vacuum tubes are heated by supply of electrical current to the positive and negative elements thereof. The grounded side is made negative by making the different potentials apply as they do in the figure, and in this manner, the different tubes function as amplifiers. A source of electrical energy is also applied to the lines to furnish the usual plate circuit energy for the tubes,'the connections being so made, that the positive current is supplied to the plate of the several tubes.

The figure is very materially different from the amplifying system now in use showing wherein it is an alternating current amplifier which furnishes direct current to a part thereof, and a decidedly different hook-up for the last stage, as it shows a single tube last stage type. However, two three electrode vacuum tubes can be used in syncro-phas'e While the foregoing specification sets forth the invention in specific terms, it is to be understood that numerous changes in connections and combinations may be involved without departing from the spirit and scope of the invention as claimed hereinafter.

Having described my invention, what I claim as new is:-

1. In an amplifying unit in combination with a transformer, rectifier and choke coil adapted to convert alternating current into substantially smooth, direct current, a radio tube having its filament connected to said source of direct current, a potentiometer, a switch associated with said potentiometer automatically operable thereby, an exciter lamp connected through said switch to said source of direct current, and a light-sensitive cell connected to said direct current source and to the input of said tube by a circuit including said potentiometer.

'2. In combination a source of rectified and filtered direct current, a vacuum tube having its filament connected to said source of direct current, a potentiometer, a switch associated with said potentiometer automatically operable thereby, a second source of rectified and filtered direct current, an exciter lamp connected through said switch to said first source of direct current and a' light sensitive cell connected to said second source of direct current and to the input of said tube, the circuit connecting the cell to the input of the tube including said potentiometer.

ALWYN D. LASSITER. 

